1. Field of the Invention
The present invention relates to embedding data in an information signal. Examples of the invention relate to: a method of and system for controlling copying of an information signal; an information signal; a data carrier on which an information signal is recorded; apparatus for modifying an information signal; a reproducing apparatus; and a computer program stored in a computer readable storage medium.
2. Description of the Prior Art
U.S. Pat. No. 5,161,210 (US Philips Corporation) discloses a system for inhibiting copying of audio signals. An audio signal is divided into frequency sub-bands and sub-band samples are quantized. The quantized samples are combined with samples of an auxiliary signal. The combined audio signal is recorded on a record carrier or transmitted. The auxiliary signal is inaudible in the combined audio signal. An audio signal reproducer having a recording unit also has a unit for detecting the auxiliary signal and generating a record control signal. The recording unit is constructed so that if a record control signal appears on its record control input the recording unit does not record the audio signal.
WO 00/51348 (Macrovision) discloses a method and apparatus for inhibiting copying of audio or video signals transmitted over a cable television or direct satellite broadcast or the Internet. The signal is protected from unwanted copying by the combination of a watermark embedded in the signal at the head end together with additional copy protection data inserted in the signal. The additional data is a ticket. If the consumer pays a fee, the signal is transmitted to the consumer. The consumer can record only if the watermark and a mathematical function of the ticket match. The function is for example a hash function.